The present invention relates to a control circuit for an on-demand ink jet printing element and to a method of dimensioning and manufacture relating thereto.
In on-demand ink jet printing, following the emission of a droplet of ink, a train of longitudinal acoustic waves is normally generated in the ink ejecting chamber, the waves being reflected by the terminal portions of the chamber. The reflection at the nozzle and the connection of the chamber to the container causes disturbances in regard to the subsequent emission of drops, which make it impossible to achieve high rates of emission.
Various remedies have been proposed in order to reduce or eliminate the effect of such reflection phenomena. A first remedy lies in using an ink which is of high viscosity but that requires the use of special highly absorbent papers. The viscosity of the ink makes it possible to reduce the effect of the reflection phenomemon only if the duct is of a certain length and for operating frequencies of lower than 3000 Hz.
Another remedy that has been proposed is that the ejection chamber should be connected to the container for the ink by means which attenuate or damp the energy of such waves. In a known arrangement, it has been proposed that a tube should be disposed between the chamber and the container, the tube being of a suitable viscoelastic material, that is to say, being such as to have an acoustic impedance equal to that of the chamber. In order for the rearward tube to absorb all the energy of the pressure, it must however be of excessive length sot that it is not possible to provide heads having a plurality of nozzles which are close together, while the junction between the emission chamber and the rearward tube promotes the generation and retention of bubbles which interfere with the subsequent emission of drops.
It has also been proposed that the length of the tube connecting the chamber to the container should be reduced, by adding thereto a concentrated resistance, for example a rigid element of an hourglass configuration, for damping the residual energy of the wave before it reaches the container. That printing element, even if it gives satisfactory results in regard to reliability and ink ejection frequency, is however rather complicated and difficult to set up and adjust.
Ways have also been proposed for eliminating the acoustic waves by means of a second pressure pulse which acts with a certain delay with respect to the expulsion pressure pulse. In a known arrangement, the second pulse is delayed for a time corresponding to the frequency of oscillation of the meniscus, which is around 2.5 KHz, so that it is not suitable for eliminating the acoustic waves of a frequency different from that of the meniscus.
In an another known arrangement, it has been proposed that the pressure wave should be suppressed by forming a duct with two separate chambers divided by a fluidic diode, and exciting a piezoelectric transducer with a second electrical pulse which is delayed with respect to the expulsion pulse. That arrangement is suited to printing elements which are connected to the container by way of a constriction, in such a way as to represent a duct which is substantially closed at both ends. That is therefore not suitable for suppressing totally the acoustic wave which derives from expulsion of the drop of ink.